The invention relates to a door latching mechanism for the door of an electric household appliance, in particular, of a washing machine, with an element of which at least a deflection part changes its spatial position upon a change in temperature of the element and thereby operates a bar element for locking and unlocking the door, as well as an electromagnetic device for unlocking the door, which comprises an actuating member.
Door latching mechanisms in washing machines serve to prevent the user from opening the machine during or shortly after the washing operation and hurting himself/herself at the rotating drum or by spilling hot water.
In commercially available door locking systems, a movable hook is provided at the door of a washing machine. Said hook is supported in a pivot and is biased in its detent direction by means of a spring which causes the hook upon closing of the door to engage the housing of the door latching mechanism which is mounted in the front wall of the washing machine. For opening the door, same is provided with a door handle, with the door hook being moved in the opening direction when pulling at the door handle, leaving the detent position, so that the door can be pulled open.
Such a door locking mechanism is advantageous in that the door can be opened even if the machine is not connected with mains. Due to the fact that without further provisions the door could be opened any time, i.e. with the washing machine running, the door is locked by means of a door latching mechanism during operation of the washing machine.
There are two popular mechanisms of door latching systems in the market. The first one of these mechanisms employs a thermal element. In such an element, a deflection part, in most cases a free end of the element, changes its spatial position upon a change in the element""s temperature, i.e. the element is bent. The mechanism is configured in such a manner that the door is locked upon this spatial change and unlocked upon the return into the original position.
Because the temperature of the element cannot be changed very rapidly, this mechanism exhibits a certain inertia upon locking and, in particular, upon unlocking. This means that after completion of the washing operating when the control unit of the washing machine provides for a temperature change and thus for unlocking of the door, the user has to wait very long until the door can be opened, even if the machine has come to a standstill.
The second popular mechanism in the market employs an electromagnet which causes a movement of a bar or slider by means of which the door is locked and unlocked. Here, the disadvantage of the thermal inertia is not given. In order to be able to open the door also in the case of a power failure, an additional mechanical emergency unlocking mechanism must be provided which is space-consuming and expensive.
From EP 0 965 677 A1 a door latching mechanism for the door of an electric household appliance is known. This door latching mechanism comprises a bimetal strip which, upon a change in temperature, varies its spatial position and thus actuates a bar element for locking and unlocking the door. The door latching mechanism further comprises an electric actuator with a solenoid and a movable actuating member. As soon as an electric current flows through the solenoid of the actuator, the actuating member cooperates with one end of a swivel arm.
The other end of the swivel arm then acts on the bar element in such a manner that the bolt element is brought from a locked position into an unlocked position. The door latching mechanism known from EP 0 965 677 A1 comprises a plurality of movable components and is therefore not only susceptible to failures but also involves high manufacturing costs.
This means that the marketable door latching mechanisms have drawbacks. It is the object of the invention to provide a door latching mechanism which does not exhibit these drawbacks.
In order to solve this object a door latching mechanism of the described type is developed in such a manner that the actuating member of the electromagnetic device immediately cooperates with the bar element or with an extension of the bar element. The inventive door latching mechanism has therefore fewer movable parts and thus a higher reliability.
The extension can be integrally formed with the bar element. Preferably, it is, however, part of a separate component which, for example, is connected with the bar element in such a manner that it extends in different directions starting from the bar element.
The actuating member can, for example, be a bolt which can be moved upon excitation or de-excitation of the electromagnetic device. If the actuating member cooperates immediately with the extension this is preferably formed as an extension of an intermediate member which, on the one side, is connected with the bar member and, on the other side, in particular via a compression spring with the deflection part of the element. The intermediate member may be a switching spring whose movement is limited by one or several stops.
A control unit is preferably provided which in the presence of an electric current, i.e. in the normal case, causes the door to be unlocked by means of the electromagnetic device comprising the electromagnet for opening, with the door being automatically unlocked by means of the element in the absence of an electric current, i.e. if the electromagnet and probably the control unit as well have failed.
According to the invention, the electromagnetic device must only unlock the door, but not lock it beforehand. The electromagnet may therefore be smaller or weaker, respectively, than with those mechanisms which in the state of the art employ an electromagnet for locking and unlocking. In particular, it can be a low-voltage or a fractional voltage magnet.
According to a preferred embodiment the electromagnet of the electromagnetic device upon its excitation will also unlock the door if it remained locked due to the change in position of the deflection part, i.e. upon the effect of the (thermal) element with the electromagnet not excited. The force action of the electromagnet is then quasi stronger than the thermal mechanism. This is advantageous in particular in cases where the washing machine it to be opened only briefly, for example to add laundry. It is then unlocked by means of the electro magnet while the thermal mechanism remains active. The door can be opened and closed shortly thereafter. After closing, the electromagnet is de-excited and the thermal mechanism can immediately relock the door.
The invention also provides a washing machine with a door latching mechanism of the above mentioned type.
According to a preferred embodiment, the washing machine comprises:
a means for interrupting a washing operation, which can be externally operated;
a sensor for sensing whether the door is open or closed; and
a control unit which effects the unlocking of the door by the electromagnetic device upon an actuation of the means and which subsequently effects that the unlocking action is cancelled and the door is locked again by the element, if the sensor has either sensed that the door was opened and closed again, that it has remained closed longer than a certain period of time and/or that a start button was pressed.
This washing machine permits a later placement of laundry, as already mentioned above. The means for an interruption is, for example, a pause button. If the user presses this pause button, the drum of the washing machine will stop. The electromagnetic device unlocks the door immediately after standstill of the drum without having to wait for the elapse of the waiting time for unlocking through the thermal mechanism. It is not even necessary to adjust the temperature of the element in such a manner that the thermal mechanism would unlock the door. As already mentioned above, the electromagnet of the electromagnetic device can be designed in such a manner that its force action is stronger than that of the thermal mechanism locking the door.
The sensor now senses if the door is opened and closed again. Subsequently, the electromagnet is de-excited. Alternatively, this is done if the door has remained closed longer than a certain time period (which is measured, for example, by means of a clock provided in the washing machine). It can also be provided that in addition a start button or another means is operated.
After the de-excitation of the electromagnet the thermal mechanism is activated again, and the still activated thermal mechanism can lock the door again, respectively. The washing operation can then be continued.
In the following, a preferred embodiment will be described with reference to schematic drawings in which: